The present invention relates generally to packaging of radioactive and/or hazardous waste in below grade trenches or excavations used for long term containment of the waste. Specifically, the present invention is an economical and efficient method for forming a waste containing monolith which meets applicable waste disposal laws, rules and regulations.
The development of effective methods for the long term disposal of radioactive and/or hazardous wastes in an efficient and economic manner has proven to be a challenging problem. A variety of unfavorable characteristics present in these wastes dictate the use of solutions and methods which insure the effective isolation of these wastes from the environment for long periods of time for health and safety reasons. These characteristics include, but are not limited to, toxicity, radioactivity, and leachability in ground water. Other characteristics which may be present in these wastes, such as corrosiveness, rule out many potential disposal schemes as viable, long term solutions.
To protect human health and the environment, the United States and foreign governments have set up a variety of laws, rules, and regulations which govern the acceptable disposal of many of these wastes. One scheme currently allowed under the laws, rules and regulations of the United States permits these wastes to be contained within concrete monoliths, which are then buried in trenches and excavations for long term disposal. Over the course of the last several years, such disposal schemes have evolved to increase the efficiency and lower the cost of disposing of wastes in this manner.
For example, in the past it was common for concrete boxes with open tops to be fabricated, and then have wastes placed inside these boxes for disposal. Concrete boxes used for in these methods were typically fabricated, either on or off site, using common concrete construction methods, whereby forms, typically fashioned of plywood or an equivalent material, were constructed to define the exterior and interior dimensions of the concrete boxes. After placing material such as reinforcing bar, for reinforcing and adding structural strength to the concrete within the interior of the forms, Portland cement and concrete additive materials were then poured in and allowed to cure. Once the concrete cured, the forms were then removed, leaving a solidified, concrete box. The thus formed concrete box was then ready for accepting waste. If fabricated off site, the concrete boxes were then placed in position within a trench or excavation, and waste was then loaded over the exterior walls of the concrete boxes, typically with a crane, and placed in the interior of the boxes. The loading of these wastes could be an expensive and time consuming process. Wastes arriving in trucks for disposal needed to be removed from the trucks and transported, typically with a crane, over the walls of the concrete boxes for placement within. The hazardous nature of the wastes dictated that stringent safety procedures be followed. Additionally, some radioactive wastes with high levels of activity dictated the use of remote handling techniques which greatly complicated the movement of the wastes from the delivery trucks, onto the cranes, and into the interior of the concrete boxes. Once the waste was placed in the interior of these concrete boxes, and a concrete top was placed over the box and the box was buried. Drawbacks of this method included very low waste loading efficiency and gaps between the boxes.
These and other drawbacks then led to the development of methods whereby the boxes were fabricated utilizing form-type construction, with one end left open. In this manner, trucks delivering waste could access the interior of the boxes without the necessity of loading wastes over the walls with a crane. Once wastes are placed in the interior of the boxes utilizing this method, the open end is then closed, by fabricating an end to the box, using the same form-type construction. The thus completed box is then filled with concrete to capture the waste in a concrete.
A large disposal site, consisting of a trench or excavation, will typically be sequentially filled with many, separately fabricated concrete monoliths repetitively formed in this manner and using common walls, thereby forming a single, large monolith. The thus formed monolith is then covered with barriers as specified in applicable laws, rules and regulations, and buried. This method of forming a series of boxes, each with an open end, loading the waste into the box, and then fabricating a form to construct a closed end, and then filling the thus formed concrete box with concrete, represents the current state of the art method for containing wastes in concrete monoliths which is allowed under current laws, rules and regulations.
However, this state of the art method poses several drawbacks which add to the overall cost and inefficiency of the process. For example, the construction of boxes using the traditional forms requires significant labor and time to build the forms. Additionally, the fabrication of an open ended box, the end for the box, and the addition of the concrete to the waste in the interior of the box, all must be performed sequentially if waste is to be loaded into the interior of the concrete boxes directly from delivery trucks, and without the use of expensive cranes and rigging and the attendant safety precautions. The cumulative time required to wait for each of the various stages to be completed, including the time for the concrete to cure in each of these sequential steps, renders the overall process for forming each concrete monolith time consuming and expensive.
Thus, there exists a need for an improved method for forming concrete monoliths containing hazardous and/or radioactive wastes which is less labor intensive, has lower cost, is less time consuming, and allows efficient covering with barriers mandated by existing laws, rules and regulations.
Accordingly, it is an object of the present invention to provide an improved method for forming a concrete monolith containing radioactive and/or hazardous wastes which minimizes the necessary labor, time and expense.
It is another object of the present invention to provide a method for forming the concrete monolith utilizing removable walls, which may be repeatedly used in the formation of other monoliths, or in the expansion of the original monolith.
It is another object of the present invention to provide a method for forming a concrete monolith utilizing removable walls, which allows for the encapsulation of waste simultaneous with the formation of the monolith, and without preformed walls to contain waste deposited therein.
It is another object of the present invention to provide a method for expanding a concrete monolith, wherein the expansion of the monolith is formed integrally with the existing monolith, and where the method allows for the encapsulation of waste simultaneous with the expansion of the monolith, and without a need for the construction of walls to contain waste deposited therein.
These and other objects are accomplished by forming a monolith containing hazardous and/or radioactive wastes by first forming an interior volume by placing removable walls on the site, pouring a flowable, curable, monolith forming material into the interior volume, thereby forming a floor within the interior volume, placing waste within the interior volume, submerging the waste within a second application of the monolith forming material by placing the second application of the monolith forming material within the interior volume, allowing the monolith forming material to cure to a solidified state, thereby forming a monolith with the waste encased within the monolith, and removing the walls. Alternatively, the floor may be first formed utilizing standard construction practices, and the method of the present invention is then practiced in the same manner as set forth above, except the removable walls are placed on top of the floor. Under either approach, the floor is typically constructed of concrete suitable for supporting the wastes placed thereon. As will be recognized by those having skill in the art, a monolith formed by the method of the present invention may also provide a suitable floor for vertical expansion of the monolith, again by utilizing the method of the present invention as set forth above. Wastes may be submerged within the flowable, curable, monolith forming material by partially filling the interior volume with a first layer of monolith forming material, allowing the first layer of monolith forming material to partially or completely cure, thereby adhering the waste to the first layer of monolith forming material, and filling the remaining interior volume with at least one additional layer of monolith forming material, thereby preventing the buoyancy of the waste from causing it to rise through the additional layer of monolith forming material. In a similar manner, several layers of waste may be added to the interior volume, with alternating layers of monolith forming materials added to anchor each successive layer in position within the interior of the monolith.
As will be recognized by those having skill in the art, once a later of monolith forming material has cured, a second layer placed thereupon typically will not bond to the first layer. Those skilled in the art have solved this problem by inserting so called cold joint dowels in the monolith forming materials which extend through each successive layer of monolith forming materials. In this manner, when a new layer is placed on top of the previously cured layer of monolith forming material, the cold joint dowels act to bind each of the two levels together. The use of removable walls thus adds another advantage to the present invention. By attaching cold joint dowel guides to the removable walls, the placement of the cold joint dowels is facilitated. As the removable walls are moved and reused, the labor necessary to place successive sets of cold joint dowels is thereby reduced, as the cold joint dowel guides are already in place, and do not have to be reattached to the removable walls. Thus, preferably, the cold joint dowel guides are attached with a hinge, allowing them to be positioned parallel to the removable walls when not in use or when the removable walls are in transit.
Wastes may be more easily placed within the interior volume if one of the removable walls is provided as having a door, thereby allowing the ingress and egress of the waste, and the use of mechanical loading of the waste with trucks, forklifts and the like. The door is then closed to hold in the monolith forming material, when added. The removable walls may be removed using any conventional means, including but not limited to hydraulic or pneumatic jacks. Removal is assisted if the interior surfaces of the removable walls are first treated with a release agent, prior to submerging the waste within the monolith forming material. In fact, the use of such release agents may eliminate the necessity of using equipment such as hydraulic, pneumatic or mechanical jacks to remove the walls. Suitable release agents include, but are not limited to, organic lubricants and plastomer sheeting. The monolith forming material may be, introduced over the top of the removable walls or through apertures provided in the sides of the removable walls. When not in use, plugs may be placed in these apertures to prevent the escape of the monolith forming materials during pouring. Preferably, the monolith forming material is vibrated as it is introduced into the interior volume, thereby preventing segregation of the constituents of the monolith forming materials. Vibration may be provided with a vibrator manifold assembly attached to the removable walls, and/or with a vibrator on the end of the pump hose used to introduce the monolith forming materials. Curing of the monolith forming material may be assisted by placing a plastomer cover over the monolith forming material, heating the monolith forming material, and/or by spraying aqueous curing fluid, or water, on the monolith forming material. Curing in cold weather may be assisted with heaters, which may be attached directly to the removable walls. The removable walls are preferably built of steel, and preferably reinforced with I-beams to provide structural rigidity. The removable walls may be free standing, or supported with braces. The braces are preferably attached to the removable walls with hinges, thereby allowing them to be folded parallel to the removable walls when being moved. Additionally, the walls may be provided with monitoring equipment attached, thereby allowing measurements including, but not limited to radioactivity or the diffusion of hazardous substances, from wastes contained within the monolith. Suitable monitoring equipment includes, but is not limited to, radiation detectors such as those available from Eberline Instruments of Sante Fe, N. Mex., and gas detection instruments, such as those available from Dynamation of Ann Arbor Mich.
Once formed, the monolith containing hazardous and/or radioactive wastes is expanded by attaching removable walls to at least one side of the monolith, thereby forming an interior volume defined by the removable walls and at least one side of the monolith, placing waste within the interior volume, submerging the waste within a flowable, curable, monolith forming material by filling the interior volume with a monolith forming material, and allowing the monolith forming material to cure to a solidified state, thereby forming an expanded monolith integral with the existing monolith. The walls are then removed, thereby leaving the waste encased within said expanded monolith and allowing the removable walls to be reused for further expansion of the monolith. When expanding an existing monlith, the removable walls are preferably attached to the monolith with removable bolts or anchors. All of the methods useful in the formation of the original monolith, including methods for submerging waste; providing a door for placing waste; methods for removing the removable walls, including treating the walls with a release agent, and hydraulic or pneumatic jacks; introducing monolith forming material over the top of the removable walls or through apertures provided in the sides of the removable walls; vibrating the monolith forming materials; and curing of the monolith forming material, are equally useful in expanding the monolith. The removable walls used in expanding the monolith are configured to allow attaching them to the existing monolith, preferably, but not meant to be limiting, with bolts or anchors. They are also preferably built of steel, and preferably reinforced with I-beams to provide structural rigidity. The removable walls used for expanding the monolith are preferably free standing, but may also be supported with braces. Braces are preferably attached to the sides of the removable walls with hinges, allowing them to be folded parallel to the removable walls when not in use, such as during transit or when the removable walls are being repositioned. Additionally, the structural rigidity of the removable walls may be enhanced with the use of stabilizing braces. Preferably, the stabilizing braces are removable, allowing them to be attached, thereby adding structural rigidity, when the removable walls are being repositioned, and removed when they might interfere with operations, such as loading the interior volume with waste or adding monolith forming materials.
As used herein, xe2x80x9cmonolith forming materialxe2x80x9d should be interpreted to include any suitable material which may be poured and will then cure to form a hardened mass capable of encasing wastes. Typically, the in practice of the present invention, monolithic forming materials will be Portland cement together with various additives, including but not limited to metal or polymer fiber, used for strengthening the monolith; metal shot for radiation shielding; natural rock and sand aggregate for cost reduction; zeolite minerals and synthetics, as well as apatite for containment capture; smectite and kaolin clays for containment capture, concrete durability and reduction of containment diffusion; fly ash for heat of hydration control, strength, and reduction of containment diffusion; blast furnace slag and silica fume for strength and reduction of containment diffusion; plasticizers for concrete pumping and handling; air entertainment agent for durability; and corrosion inhibitors for internal metal waste package longevity. As a practical matter, the specific wastes being disposed will dictate the appropriate additives for a each monolith, and the location of the monolith being formed will effect the availability and thus the price of the various constituents of the monolithic forming materials and additives which may be used as substitutes for one and another. The exact combination of monolithic forming materials will thus typically be selected as the lowest cost material which will still meet applicable laws, rules and regulations. Those having skill in the art are well versed in the particular combinations and ratios of additives appropriate for the various wastes which may be disposed of using the present invention, as well as the applicable laws, rules and regulations which will govern their disposal. No further discussion of these monolithic materials and the various additives is therefore necessary to enable those having skill in the art to practice the best mode of the present invention.